MAOAteacher Slides

8/13/2019 MAOAteacher Slides

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Genes, environment and

antisocial behaviour

The science and issues


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An early model: Genes vs.

environment

Jason is always getting

into trouble

Im sure it

runs in th e

family . . .

it must be

the way he was

brou ght up . .

.


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Risk factors for antisocial behaviour

Having an aggressive father Having divorced parents

Poverty

Subject to inconsistent discipline

Being born to a teenage mother Being reared in a family of at

least four children

Growing up with antisocial peers or adults (a criminal

father, young role models) Being thrill-seeking, interested in danger, enjoy taking

risks.

The right genotype?


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Nature and nurture

The research team (UK and New Zealand)reported new evidence of a "gene byenvironment" interaction: a genetic variant

is associated with different antisocialoutcomes among maltreated children.

This was the first convincing evidence ofthe complex interplay of genetic andenvironmental influences on behaviour in

humans.

This evidence has since been supported inmore than three other studies, butunsupported by one.

In August 2002 a ground-breaking study was published in the prestigiousAmerican journal, Science.


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The new model: G x E

(genes by environment)

Jason is always getting

into trouble

it must be a combination

of his g enes and

the way he was brough t up

. . .


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The science . . .


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Key studies in the 1990s

Brunner et al (1993). Genetic and metabolic studies on a large family where

males are affected by a syndrome (borderline retardation and abnormal

behaviour inc. impulsive aggression). The affected males were found to have a

truncated (shortened) monoamine oxidase A (MAOA) protein.

Conclusion: MAOA deficiency disturbed regulation of impulsive aggression

Cases et al (1995), Shih et al (1999).

Created transgenic mice lacking MAOA activity (induced a deletion in thegene). Males had significant increase in brain levels of neurotransmitters

serotonin and norepinephrine and exhibited enhanced aggression. Studies

suggested a lack of MAOA expression in the forebrain, which could be

reversed in young animals, but not in adults.

Backtrack:

Of knock-out mice and aggressive men


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X-linkage

Source: Indigo Instruments, www.indigo.com

Genetic conditions caused by changes on the

X chromosome are called sex-linked (or X-

linked). Mutations on X chromosomes are

consequently far more likely to affect men

than women.

Males have only one copy of the X

chromosome, whereas females have two

copies. If a change (mutation) occurs in a

gene on a mans X chromosome, there is no

other copy of the gene to compensate.


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A gene for violence?

Researchers have attempted to find

a connection between the levels of

MAOA produced by individuals and

behaviour such as violence,

alcoholism, depression and bipolar

disease.

However, none of these studies was

able to show a convincing link the

behaviour was apparently too

complex to be controlled by a single

gene.


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The Dunedin connection

The Dunedin Multidisciplinary

Health and Development study

1037 children (52% male) born in

Dunedin between April 1972 andMarch 1973.

Subjects assessed at ages 3, 5, 7,

9, 11, 13, 15, 18, 21 and 26 years.

DNA swabs taken at age 26.

Source: Google Earth, http://earth.google.com/
http://earth.google.com/http://earth.google.com/


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boys who had a high

risk . . . a low activityMAOA genotype on the

genetic test . . . and had

been maltreated, were

only about 10% of the

boys in the study but

accounted for almost40% of the crimes that

had been committed.

the boys who had been

maltreated, who had the

high-activity MAOAgenotype seemed to be

protected against

maltreatment . . .

Source: Caspi et al (2002), Science, 297, 851-854;

interview with co-author Professor T. Moffitt

The 2002 Science paper


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Could the following have an effect?

Could the high MAOA activity protective effect be brought about:

if children with this genotype were likely to be reared in favourable

environments?

No social class differences were found between males with low and

high MAOA activity

because of individual differences in IQ.

No IQ differences were found between males with low- and high

MAOA activity


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Some issues about applications:

How reliable would a test be?

Would a treatment have side effects?

How antisocial is antisocial enough?

Who should be tested(how much maltreatment is too much?)

Could MAOA levels become a defence in court?

Is a protected child less worthy of help after maltreatment?

Should testing be required; is there at time when benefits to societyoverride the rights of an individual?

Source: Wellcome Trust

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